Submitted to: Journal of Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/26/2010
Publication Date: 5/11/2011
Citation: Fernandez-Sainz, I.J., Holinka-Patterson, L.G., Gladue, D.P., O'Donnell, V., Lu, Z., Gavrilov, B.K., Risatti, G.R., Borca, M.V. 2011. Substitution of specific cysteine residues in E1 glycoprotein of classical swine fever virus strain Brescia affects formation of E1-E2 heterodimers and alters virulence in swine. Journal of Virology. 407:129-136. Interpretive Summary: Classical swine fever virus (CSFV) has four proteins forming the structure of the virus particle: Core, E0, E1 and E2. Core protein forms the capside of the virus, surrounding and protecting virus genome while the other three are part of the external layer (envelope) of the virus particle. E1 can be presented as monomer or linked to a molecule of E2. This interaction is mediated by a specific type of amino acid residue named Cystein (CysR). A molecule of E1 contains six CysR but it is unknown which ones are involved in the interaction with E2, and the possible function of these CysR has been largely ignored in virus biology. In this report we identify the two CysR critical for the interaction with E2, and also show that that these two CysR are critical for the production of disease in swine. Additionally, we show that a genetically engineered virus, having deleted these two critical CysR, can be used as live attenuated vaccine as it induces complete protection against the infection with a very virulent virus.
Technical Abstract: E1, along with E^rns and E2, is one of the three envelope glycoproteins of Classical Swine Fever Virus (CSFV). E1 and E2 are anchored to the virus envelope at their carboxyl termini and E^rns loosely associates with the viral envelope. In infected cells, E2 forms homodimers and heterodimers with E1, mainly mediated by disulfide bridges between cysteine residues. CSFV strain Brescia E1 protein possesses six cysteine residues at positions 5, 20, 24, 94, 123, and 171. The role of these residues in the formation of E1-E2 heterodimers and their effect on CSFV cycle in vitro and in vivo remain unclear. Here we observed that recombinant mutant viruses harboring individual cysteine to serine substitutions in E1 envelope protein neither altered formation of E1-E2 heterodimers nor affected virus progeny yields in infected primary swine cells. These single cysteine mutant viruses were virulent in infected swine. A double mutant harboring Cys24Ser and Cys94Ser substitutions in E1 protein altered formation of E1-E2 heterodimers in infected cells. This recombinant virus, E1DeltaCys24/94v, showed delayed growth kinetics in primary swine macrophage cultures and was attenuated in swine. Furthermore, infection with E1DeltaCys24/94v effectively protected swine from challenge with virulent BICv at 3 and 28 days post-infection.